The invention relates to external connectors, or tie bars, for connecting two marine propulsion devices. Such tie bars aid in keeping the propulsion devices in parallel relation when they are subjected to steering torque or other hydrodynamic forces.
It would be desirable to have two drive units connected by a tie bar outboard of the boat and still be able to tilt either drive unit to its full tilt up position while maintaining the other drive unit in the full down position if, for instance, the other drive unit were disabled and the associated water craft must be brought back to the harbor on one engine.
In the past, tie bars have generally been nonextendable once they were adjusted to the proper length between a pair of mounted marine propulsion devices. For example, the devices depicted in U.S. Pat. Nos. 3,756,186 and 4,311,471 have such a characteristic.
Since their length was fixed, devices such as those shown in the prior art generally did not allow for the upward tilting of one marine propulsion device with respect to the other device without rotation of one unit relative to another unit about a vertical axis.
One exception is found in U.S. Pat. No. 4,311,471, especially FIGS. 5 and 6, where the two propulsion units are not positioned so as to rotate about coaxial horizontal axes, but are instead displaced vertically on the transom. The two propulsion units are in alignment to drive the boat forward when the lower unit is tilted either up or down because the tie bar ends up at an equal angle above or below the horizontal. It can be appreciated that if the upper unit were attempted to be tilted upwardly while the lower unit is in the down position, there would have to be relative rotation of the units about their vertical axes. Moreover, if both units were mounted on the transom about coincident axes, neither could be tilted without relative rotation about their vertical axes.
One attempt to provide means to solve this problem is found in U.S. Pat. No. 4,310,320. In this patent an electrical system is described which contains a control circuitry which requires both drive units to be tilted up or down after a certain angle of tilt.
Attention is also directed to the following patents:
U.S. Pat. No. 1,454,973 PA1 U.S. Pat. No. 3,197,191 PA1 U.S. Pat. No. 4,416,636 PA1 U.S. Pat. No. 4,300,888 PA1 U.S. Pat. No. 3,339,680